Portion of a sole bottom surface



FIG. 1 is a bottom plan view of a portion of a side bottom surface showing my new design; and,

FIG. 2 is an enlarged cross-sectional view taken on line 2--2 of FIG. 1.

The broken line showing of the remainder of the sole outsole is for illustration purposes only and forms no part of the claimed design. 

The ornamental design for a portion of sole bottom surface, as shown and descirbed. 